diff --git a/decomp.h b/decomp.hpp
similarity index 66%
rename from decomp.h
rename to decomp.hpp
index 98a35d2d..4a863d24 100644
--- a/decomp.h
+++ b/decomp.hpp
@@ -1,6 +1,6 @@
 /* ReC98
  * -----
- * Macros to help decompiling the seemingly impossible
+ * Macros and inline functions to help decompiling the seemingly impossible
  */
 
 // Flag comparisons
@@ -55,48 +55,48 @@
 //
 // Also, hey, no need for the MK_FP() macro if we directly return the correct
 // types.
-#ifdef __cplusplus
+
+} // extern "C" was a mistake
+
+#if defined(__TURBOC__) && defined(__MSDOS__)
+	// Declared in <dos.h> in these compilers.
+	void __emit__(uint8_t __byte, ...);
+#endif
+
+struct Decomp_ES { void  __seg* value() { return (void  __seg *)(_ES); } };
+struct Decomp_FS { void  __seg* value() { return (void  __seg *)(_FS); } };
+struct Decomp_GS { void  __seg* value() { return (void  __seg *)(_GS); } };
+struct Decomp_DI { void __near* value() { return (void __near *)(_DI); } };
+
+// Removing [val] from the parameter lists of the template functions below
+// perfects the inlining.
+#define poked(sgm, off, val) \
+	_EAX = val; \
+	poked_eax((Decomp##sgm *)NULL, (Decomp##off *)NULL, (uint8_t)(0x89));
+
+#define poke_or_d(sgm, off, val) \
+	_EAX = val; \
+	poked_eax((Decomp##sgm *)NULL, (Decomp##off *)NULL, (uint8_t)(0x09));
+
+template <class Segment, class Offset> inline void poked_eax(
+	Segment *sgm, Offset *off, uint8_t op
+) {
+	if(op == 0x89) {
+		*(uint32_t far *)(sgm->value() + off->value()) = _EAX;
+	} else if(op == 0x09) {
+		*(uint32_t far *)(sgm->value() + off->value()) |= _EAX;
+	}
 }
-	#if defined(__TURBOC__) && defined(__MSDOS__)
-		// Declared in <dos.h> in these compilers.
-		void __emit__(uint8_t __byte, ...);
-	#endif
 
-	struct Decomp_ES { void  __seg* value() { return (void  __seg *)(_ES); } };
-	struct Decomp_FS { void  __seg* value() { return (void  __seg *)(_FS); } };
-	struct Decomp_GS { void  __seg* value() { return (void  __seg *)(_GS); } };
-	struct Decomp_DI { void __near* value() { return (void __near *)(_DI); } };
+inline void poked_eax(Decomp_FS *sgm, Decomp_DI *off, uint8_t op) {
+	__emit__(0x66, 0x64, op, 0x05); // [op] FS:[DI], EAX
+}
 
-	// Removing [val] from the parameter lists of the template functions below
-	// perfects the inlining.
-	#define poked(sgm, off, val) \
-		_EAX = val; \
-		poked_eax((Decomp##sgm *)NULL, (Decomp##off *)NULL, (uint8_t)(0x89));
-
-	#define poke_or_d(sgm, off, val) \
-		_EAX = val; \
-		poked_eax((Decomp##sgm *)NULL, (Decomp##off *)NULL, (uint8_t)(0x09));
-
-	template <class Segment, class Offset> inline void poked_eax(
-		Segment *sgm, Offset *off, uint8_t op
-	) {
-		if(op == 0x89) {
-			*(uint32_t far *)(sgm->value() + off->value()) = _EAX;
-		} else if(op == 0x09) {
-			*(uint32_t far *)(sgm->value() + off->value()) |= _EAX;
-		}
-	}
-
-	inline void poked_eax(Decomp_FS *sgm, Decomp_DI *off, uint8_t op) {
-		__emit__(0x66, 0x64, op, 0x05); // [op] FS:[DI], EAX
-	}
-
-	inline void poked_eax(Decomp_GS *sgm, Decomp_DI *off, uint8_t op) {
-		__emit__(0x66, 0x65, op, 0x05); // [op] GS:[DI], EAX
-	}
+inline void poked_eax(Decomp_GS *sgm, Decomp_DI *off, uint8_t op) {
+	__emit__(0x66, 0x65, op, 0x05); // [op] GS:[DI], EAX
+}
 
 extern "C" {
-#endif
 // ---------------------------------------------------------
 
 // 32-bit ASM instructions not supported by Turbo C++ 4.0J's built-in
diff --git a/th01/end/pic.cpp b/th01/end/pic.cpp
index 2a100b08..f192d9e4 100644
--- a/th01/end/pic.cpp
+++ b/th01/end/pic.cpp
@@ -10,7 +10,7 @@ void pascal end_pics_load_palette_show(const char *fn)
 
 // Avoid symbol duplication...
 #define egc_start_copy egc_start_copy_1
-#include "th01/hardware/egcstart.c"
+#include "th01/hardware/egcstart.cpp"
 
 static const pixel_t PIC_W = (RES_X / 2);
 static const pixel_t PIC_H = (RES_Y / 2);
diff --git a/th01/hardware/egcrect.cpp b/th01/hardware/egcrect.cpp
index 338fd007..44e859f9 100644
--- a/th01/hardware/egcrect.cpp
+++ b/th01/hardware/egcrect.cpp
@@ -1,4 +1,4 @@
-#include "th01/hardware/egcstart.c"
+#include "th01/hardware/egcstart.cpp"
 
 void egc_copy_rect_1_to_0_16(screen_x_t x, vram_y_t y, pixel_t w, pixel_t h)
 {
diff --git a/th01/hardware/egcstart.c b/th01/hardware/egcstart.cpp
similarity index 81%
rename from th01/hardware/egcstart.c
rename to th01/hardware/egcstart.cpp
index 69361fc8..c3fca280 100644
--- a/th01/hardware/egcstart.c
+++ b/th01/hardware/egcstart.cpp
@@ -1,5 +1,5 @@
+#include "decomp.hpp"
 #include "th01/hardware/egc.h"
-#include "decomp.h"
 
 void pascal egc_start_copy(void)
 {
diff --git a/th01/main_13.cpp b/th01/main_13.cpp
index 2fcba9ef..507ed01d 100644
--- a/th01/main_13.cpp
+++ b/th01/main_13.cpp
@@ -10,7 +10,7 @@ extern "C" {
 #include "platform.h"
 #include "pc98.h"
 #include "planar.h"
-#include "decomp.h"
+#include "decomp.hpp"
 #include "master.hpp"
 #include "th01/hardware/egc.h"
 #include "th01/hardware/graph.h"
diff --git a/th01/zunsoft.cpp b/th01/zunsoft.cpp
index ab568789..a0bb747d 100644
--- a/th01/zunsoft.cpp
+++ b/th01/zunsoft.cpp
@@ -7,7 +7,7 @@ extern "C" {
 #include "platform.h"
 #include "x86real.h"
 #include "pc98.h"
-#include "decomp.h"
+#include "decomp.hpp"
 #include "master.hpp"
 #include "th01/hardware/egc.h"
 #include "th01/math/vector.hpp"
diff --git a/th03/formats/mrs.cpp b/th03/formats/mrs.cpp
index befd44df..0173ba7c 100644
--- a/th03/formats/mrs.cpp
+++ b/th03/formats/mrs.cpp
@@ -6,7 +6,7 @@ extern "C" {
 #include "platform.h"
 #include "pc98.h"
 #include "planar.h"
-#include "decomp.h"
+#include "decomp.hpp"
 #include "master.hpp"
 #include "th03/formats/hfliplut.h"
 }
diff --git a/th03/sprite16.cpp b/th03/sprite16.cpp
index 26a2374f..c7ccf063 100644
--- a/th03/sprite16.cpp
+++ b/th03/sprite16.cpp
@@ -11,7 +11,7 @@ extern "C" {
 #include "x86real.h"
 #include "pc98.h"
 #include "planar.h"
-#include "decomp.h"
+#include "decomp.hpp"
 #include "master.hpp"
 #include "libs/sprite16/sprite16.h"
 #include "th03/sprite16.hpp"
diff --git a/th04/end/box.cpp b/th04/end/box.cpp
index 8ccfa275..61c4884d 100644
--- a/th04/end/box.cpp
+++ b/th04/end/box.cpp
@@ -2,7 +2,7 @@
 #include "x86real.h"
 #include "pc98.h"
 #include "planar.h"
-#include "decomp.h"
+#include "decomp.hpp"
 #include "twobyte.h"
 #include "master.hpp"
 
diff --git a/th04/hardware/egcrect.cpp b/th04/hardware/egcrect.cpp
index a3771ead..d3adb5c2 100644
--- a/th04/hardware/egcrect.cpp
+++ b/th04/hardware/egcrect.cpp
@@ -5,7 +5,7 @@ extern "C" {
 #include "x86real.h"
 #include "pc98.h"
 #include "planar.h"
-#include "decomp.h"
+#include "decomp.hpp"
 #include "master.hpp"
 #include "th01/hardware/egc.h"
 
diff --git a/th05/formats/cdg_p_nc.cpp b/th05/formats/cdg_p_nc.cpp
index 548c11cf..af6d7e96 100644
--- a/th05/formats/cdg_p_nc.cpp
+++ b/th05/formats/cdg_p_nc.cpp
@@ -6,7 +6,7 @@ extern "C" {
 #include "x86real.h"
 #include "pc98.h"
 #include "planar.h"
-#include "decomp.h"
+#include "decomp.hpp"
 #include "th04/formats/cdg.h"
 }
 
diff --git a/th05/formats/pi_impl.hpp b/th05/formats/pi_impl.hpp
index 2602e3e6..6c111485 100644
--- a/th05/formats/pi_impl.hpp
+++ b/th05/formats/pi_impl.hpp
@@ -1,6 +1,6 @@
 // Shared parts of the pi_put_*() functions.
 
-#include "decomp.h"
+#include "decomp.hpp"
 
 inline void imul_di(int8_t factor) {
 	__emit__(0x6B, 0xFF, factor);
diff --git a/th05/hardware/inp_h_w.cpp b/th05/hardware/inp_h_w.cpp
index 66f8c8ca..52511f4d 100644
--- a/th05/hardware/inp_h_w.cpp
+++ b/th05/hardware/inp_h_w.cpp
@@ -2,7 +2,7 @@
 
 extern "C" {
 #include "platform.h"
-#include "decomp.h"
+#include "decomp.hpp"
 #include "master.hpp"
 #include "th05/hardware/input.h"
 }
diff --git a/th05/music/piano_c.cpp b/th05/music/piano_c.cpp
index 7bec50a9..0a497df0 100644
--- a/th05/music/piano_c.cpp
+++ b/th05/music/piano_c.cpp
@@ -6,7 +6,7 @@ extern "C" {
 #include "x86real.h"
 #include "pc98.h"
 #include "planar.h"
-#include "decomp.h"
+#include "decomp.hpp"
 #include "master.hpp"
 #include "libs/kaja/kaja.h"
 #include "th05/music/piano.h"
diff --git a/th05/snd/load.cpp b/th05/snd/load.cpp
index 1f4f57a4..b1214c7d 100644
--- a/th05/snd/load.cpp
+++ b/th05/snd/load.cpp
@@ -5,7 +5,7 @@ extern "C" {
 #include <errno.h>
 #include "platform.h"
 #include "x86real.h"
-#include "decomp.h"
+#include "decomp.hpp"
 #include "master.hpp"
 #include "libs/kaja/kaja.h"
 #include "th05/snd/snd.h"